Regarded ontologically, the internal place of a body is an absolute accident: it is the accident which gives the latter concrete volume or external extension, and it is not really distinct from the latter. The external place of a body includes in addition the spatial relations of the latter to other bodies, relations grounded in the volumes of those bodies.
It is by reason of these spatial relations with certain bodies, that a being is said to be “present” in a certain place. A corporeal extended substance is said to occupy space circumscriptivé, or by having parts outside parts in the place it occupies. A finite or created spiritual substance is said to occupy space definitivé inasmuch as it can naturally exercise its influence only within certain more or less extended spatial limits: as the human soul does within the confines of the body.[368] The Infinite Being is said to occupy space repletivé. The actual presence of God in all real space, conserving in its existence all created, contingent reality, is called the Divine Ubiquity. The perfection whereby God can be present in other worlds and other spaces which He may actualize is called the Divine Immensity.
The local presence of a finite being to other finite beings is itself a positive perfection—based on its actual extension if it be an extended corporeal substance, or on its power of operating within a certain space if it be a spiritual substance. The fact that in the case of a finite being this local presence is itself limited, is at once a corollary and an index of the finiteness of the being in question. Only the Infinite Being is omnipresent or ubiquitous. But every finite being, whether corporeal or spiritual, from the very fact that it exists at all, must exist somewhere or have some locus internus, and it must have some local presence if there are other corporeal, extended beings in existence. Thus the local presence of a being is a (finite) perfection which seems to be grounded in the very nature itself of the creature.[369]
From the concept of place we pass naturally to the more complex and abstract notion of space. It is, of course, by cognitive processes, both sentient and intellectual, that we come into possession of the abstract concept of space. These processes are subjective [pg 320] in the sense that they are processes of the individual's mental faculties. Distinguishing between the processes and the object or content which is brought into consciousness, or put in presence of the mind, by means of them; and assuming that this object or content is not a mere form or groove of our cognitive activity, not a mere antecedent condition requisite on the mental side for the conscious exercise of this activity on its data, but that on the contrary it is, or involves, an objective, extramental reality apprehended by the mind,—we go on to inquire in what this objective reality consists. In approaching the question we must first note that what is true of every abstract and universal concept is true of the concept of space, viz. that the abstractness and universality (“intentio universalitatis”) of real being, as apprehended by the intellect, are modes or forms of thought, entia rationis, logical conditions and relations which are created by thought, and which exist only in and for thought; while the reality itself is the object apprehended in these modes and under these conditions: Universale est formaliter in mente et fundamentaliter in re. Now through the concept of space we apprehend a reality. Our concept of real space has for its object an actual reality. What is this reality? If space is real, in what does its reality consist? We answer that the reality which we apprehend through this concept is the total amount of the actual extension or magnitude of all created and coexisting bodies; not, however, this total magnitude considered absolutely and in itself, but as endowed with real and mutual relations of all its parts to one another,[370] relations which are apprehended by us as distances, linear, superficial, and voluminal.
Such, then, is the reality corresponding to our concept of real and actual space. But no sooner have we reached this concept than we may look at its object in the abstract, remove mentally all limits from it, and conceive all extended bodies as actually non-existent. What is the result? The result is that we have now present to our minds the possibility of the existence of extended bodies, and a concomitant imagination image (which memory will not allow us to banish from consciousness) of a vast and boundless emptiness, an indefinite and unmeasurable vacuum in which bodies were or may be. The intellectual concept is now not a concept of any actual object, but of a mere possibility: the possibility of a corporeal, extended universe. This is the [pg 321] concept of what we call ideal or possible space; and like the concept of any other possible reality it is derived by us from our experience of actual reality,—in this case from our experience of extended bodies as actually existing. The corporeal universe has not existed from all eternity, but it was possible from all eternity. When we think of that possibility as antecedent to all creation, we are thinking of bodies, and of their extension, as possible; and the concept of their total extension as possible is the concept of ideal or possible space. This concept is, through a psychological necessity, accompanied by an imagination image of what we call imaginary space: the unlimited vacuity which preceded corporeal creation, which would still persist were the latter totally annihilated, which reaches out indefinitely beyond its actual limits, which imagination pictures for us as a receptacle in which bodies may exist but which all the time our reason assures us is actually nothing, being really only the known possibility of corporeal creatures. This familiar notion of an empty receptacle for bodies is what we have in mind when we think of bodies as existing “in space”. Hence we say that space, as conceived by the human mind, is not a mere subjective form of cognition, a mere ens rationis, inasmuch as our concept has a foundation in reality, viz. the actual extension of all existing bodies; nor is it on the other hand simply a real entity, because this actual extension of bodies does not really exist in the manner in which we apprehend it under the abstract concept of space, as a mere possibility, or empty receptacle, of bodies. Space is therefore an ens rationis cum fundamento in re.
A great variety of interesting but abstruse questions arise from the consideration of space; but they belong properly to Cosmology and Natural Theology. For example: Is real space actually infinite in magnitude, or finite? In other words, besides the whole solar system—which is in reality merely one star plus its planets and their satellites,—is there in existence an actually infinite multitude of such stellar worlds? It is not likely that this can ever be determined empirically. Many philosophers maintain that the question must be answered in the negative, inasmuch as an actually infinite multitude is impossible. Others, however, deny that the impossibility of an actually infinite multitude can be proved.[371] Again, within the limits of the actual corporeal universe, are there really vacant spaces, or is all space within these limits actually (or even necessarily) filled with an all-pervading ether or corporeal medium of some sort? How would local motion be possible if all space were full of impenetrable matter? How would the real interaction of [pg 322] distant bodies on one another be possible if there were only vacant space between them? Is the real volume or extension of a corporeal substance (as distinct from its apparent volume, which is supposed to include interstices, or spaces not filled with that body) actually or necessarily unchangeable? Or is the internal quantity of a body actually or necessarily unchangeable? Can more than one individual corporeal substance simultaneously occupy exactly the same space? (This is not possible naturally, for impenetrability is a natural consequence of local extension; but it is possible miraculously—if all the bodies, or all except one, be miraculously deprived of local or spatial extension.) Can the same individual body be present at the same time in totally different and distant places? (Not naturally, of course; but how it can happen even miraculously is a more difficult question than the preceding one. It is in virtue of its actual or local extension that a body is present sensibly in a definite place. Deprived miraculously of this extension it can be simultaneously in several places, as our Blessed Lord's Body is in the Eucharist. But if a body has its natural local extension at one definite place, does this extension so confine its presence to this place that it cannot be simultaneously present—miraculously, and without its local extension—at other places? The most we can say is that the absolute impossibility of this is neither self-evident nor capable of cogent proof. The Body of our Lord has its natural local extension in heaven—for heaven, which will be the abode of the glorified bodies of the blessed after the general resurrection, must be not merely a state or condition, but a place—and at the same time it is sacramentally present in many places on earth.)
85. Time: its Apprehension and Measurement.—If the concept of space is difficult to analyse, and gives rise to some practically insoluble problems, this is still more true of the concept of time. “What, then, is time?” exclaims St. Augustine in his Confessions.[372] “If no one asks me, I know; but if I am asked to explain it, then I do not know!” We reach the notion of space through our external perception of extension by the senses of sight and touch. So also we derive the notion of time from our perception of motion or change, and mainly from our consciousness of change and succession in our own conscious states. The concept of time involves immediately two other concepts, that of duration, and that of succession. Duration, or continuance in existence, is of two kinds, permanent and successive. Permanent duration is the duration of an immutable being, formally and in so far as it is immutable. Successive duration is the continued existence or duration of a being that is subject to change, formally and in so far as it is mutable. Now real change involves a continuous succession of real states, it is a continuous process or fieri; and it is the duration of a being subject [pg 323] to such change that we call time or temporal duration. Had we no consciousness of change, or succession of states, we could have no notion of time; though we might have a notion of unchanging duration if per impossibile our cognitive activity were itself devoid of any succession of conscious states and had for its object only unchanging reality. But since our cognitive activity is de facto successive we can apprehend permanent or unchanging duration, not as it is in itself, but only after the analogy of successive or temporal duration ([86]). The continuous series of successive states involved in change is, therefore, the real and objective content of our notion of time; just as the co-existing total of extension forms the content of our notion of space. The concept of space is the concept of something static; that of time is the concept of something kinetic. Time is the continuity of change: where there is change there is time; without change time would be inconceivable. Change involves succession, and succession involves the temporal elements of “before” and “after,” separated by the indivisible limiting factor called the “now” or “present instant”. The “past” and the “future” are the two parts of time, while the “present instant” is not a part of time, but a point of demarcation at which the future flows into the past. Change is a reality; it is a real mode of the existence of mutable things; but neither the immediately past state, nor the immediately future state of a changing reality, are actual at the present instant: it is only to the permanent, abiding mind, apprehending real change, and endowed with memory and expectation, that the past and the future are actually (and, of course, only ideally, not really) present. And it is only by holding past and future in present consciousness, by distinguishing mentally between them, by counting or measuring the continuous flow of successive states from future to past, through the present instant, that the mind comes into possession of the concept of time.[373] The mind thus apprehends time as the measure of the continuous flow of successive states in things subject to change. As thus apprehended, time is not merely the reality of change: it is the successive continuity or duration of change considered as a measure of change. It is that within which all changes are conceived to happen: just as space is conceived as that within [pg 324] which all extended things are conceived to exist. We have said that without real change or motion there could be no time. We can now add that without a mind to apprehend and measure this motion there could be no time. As St. Thomas declares, following Aristotle: Si non esset anima non esset tempus.[374] For time, as apprehended by means of our abstract and universal concept, is not simply a reality, but a reality endowed with logical relations, or, in other words, a logical entity grounded in reality, an ens rationis cum fundamento in re.
This brings us to Aristotle's classic definition,[375] which is at once pithy and pregnant: Τοῦτο γάρ ἐστιν ὁ χρόνος, ἀριθμὸς κινήσεως κατὰ τὸ πρότερον καὶ ὓστερον: Tempus est numerus motus secundum prius et posterius: Time is the measure of motion or change by what we conceive as before and after, or future and past, in its process. Every change involves its own intrinsic flow of states from future to past. It is by mentally distinguishing these states, and by thus computing, counting, numbering, the continuous flow or change, that we derive from the latter the notion of time.[376] If, then, we consider all created things, all things subject to change, we shall realize that real time commenced with the creation of the first of them and will continue as long as they (or any of them) continue to exist. We thus arrive at a conception of time in general, analogous to that of space: the whole continuous series of successions, in changing things, from future to past, regarded as that in which these changes occur, and which is the measure of them.
Here, too, as in the case of space, we can distinguish real time, which is the total duration of actual changes, from ideal or imaginary time which is the conceived and imagined duration of merely possible changes.
But a more important distinction is that between intrinsic or internal time, or the duration of any concrete mutable reality considered in itself, and extrinsic or external time, which is some other extrinsic temporal duration with which we compare, and by which [pg 325] we may measure, the former duration. Every change or motion has its own internal time; and this is what we have been so far endeavouring to analyse. If two men start at the same instant to walk in the same direction, and if one walk three miles and the other four, while the hands of a watch mark the lapse of an hour, the external time of each walk will be the same, will coincide with one and the same motion of the hands of the watch used as a measure. But the internal time of the four-mile walk will be greater than that of the three-mile walk. The former will be a greater amount of change than the latter; and therefore its internal time, estimated by this amount absolutely, will be greater than that of the latter estimated by its amount absolutely.[377] The greater the amount of a change the greater the internal time-duration or series of successive states which measures this change absolutely.[378]